SDK / exoplayer

Follow-up on the update to ABR logic in AdaptiveTrackSelection for live
streaming case:
- Do not reset liveEdgeTimeUs when user seek to a different position.
- For HlsChunkSource, for non-independent segments, currently the
bufferedDuration calculate will subtract previousChunk's duration. So to make
it work with live-streaming ABR logic, we subtract timeToLiveEdgeUs a similar
amount to compensate for that operation.
- Minor update to DefaultSSChunkSource, only perform TrackSelection when needed
(after checking necessary conditions).

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=169531275